Arrangement of air heaters, feed water heaters, and superheaters in steam generators



Au 26, 1952 J. v. PYLE 60 8 ARRANGEMENT OF AIR HEATERS, FEED WATER HEATERS, AND I SUPERHEATERS IN STEAM GENERATORS Flled Feb 2, 1946 INVENTOR J OHN V P YLE BY [ATTORNEYS Patented Aug. 26, 1952 "UNITED STATES. i-hd'lENT GFFICE ARRANGEIWENT OF AIR HEATERS, FEED WATER HEATERS, AND SUEERHEATERS IN STEAM GENERATORS John V. Pyle,-Briar Cliii' Manor, N. Y., assignor to Kennedy-Van Saun Mfg. & Eng. Corporation, New York, N. Y., a corporation of Delaware Application February 2, 1946, Serial No. 645,222

3 Claims. (01. 122-1) 1 My invention relates to improvements in methods of firing steam generators with atomized or pulverized fuels, and more particularly with pulverized anthracite coal, and to an improved steam generator unit.

Considerable difiiculty has been experienced with large steam generator units of the power plant type in attempts to utilize pulverized anthracite coal. One of the difficulties arises from the apparent inability to maintain a sufficiently high temperature adjacent the point of introduction of the coal. Other difficulties have apparently been due to the variable degree of wetness of the coal, particularly with" the finest sizes which may tend to be hygroscopic.

I have discovered that these and other difficulties arising from attempts to use pulverized anthracite coal may be largely avoided. by regulating the temperature of the preheated air used in the grinding mill for drying and picking up the pulverized coal. I have also discovered that the burning of pulverized anthracite coal may be effectively promoted by balancing the draft in the combustion chamber so as to increase the turbulenc'e'and circulation of the furnace gases adjacent the burners. I furthermore control the movement of combustion gases away from the area of the burners and provide a pressure gra dient so as to aid in maintaining high combustion temperatures. 1'

In accordance with my invention, I employ the foregoing and other control means in the burning of anthracite coal. or other fuels and find that I am able to substantially reduce the'proportion of unburned carbon in the flue gases}: .In' previous attempts to utilize pulverized anthracite coal, considerable difficulty has arisen because of thefailwe to burn large proportions vof the pulverized coal which is carriedin thecombustion gas stream and which not only'fouls up the generatorunit but also creates a public nuisance if discharged to the atmosphere. T. i According to my invention, the improved steam generator unit, which is particularly. adapted for powerplant use, comprises an installation including a downdraft combustion chamber, the walls of which are comprised of closely mounted steam tubes. a chamber in which the steam produced inthe unit is superheated in'a tube bank,

an economizer tube bank in which water sup,-

tioned elements: are utilized for I preheating air.

The unit also preferably includes a tube mill in which the anthracite or other coal to be burned in the generator unit is pulverized and to which is supplied preheated air from the airpreheater. The unit is provided with suitable burners on the top of the combustion chamber for burning pulverized coal and meansfor conducting a stream of preheated air and pulverized coal directly from the tube mill to the burners of the combustion chamber. i

According to a preferred form of my invention, suitable control means are provided for controlling the combustion in the upper portion of the combustion chamber including an exhaustif an for combustion gases which is regulated in accordance with the pressure or temperature, or both, in the upper portion of the combustion chamber. Other control means are provided for combustion gas flow from the steam superheater in accordance with the temperature of the superheated steam discharged from the superheater. A bypass control is provided for shunting high temperature combustion gases directly from the superheater to the air preheaterin accordance with the temperature of the preheated air, to control the air temperature.

I have found that the use of air at a very big temperature is very eifective inthe .grinding of anthracite coal, particularly. when'the coal is abnormally wet. Furthermore, air at a very high temperature aids in boosting the temperature in the combustion chamber and in effecting the complete combustion of pulverized anthracite coal.

According toan important feature of my invention, I have devised an improved method for utilizing pulverized coal, particularly anthracite coal, in the firing of steam generator units such as the power plant type. In generalthi method is preferably. applied in a substantially. complete generator unit, including a combustion chamber, a steam superheating chamber in which a bank of superheating tubes is mounted, an economizer tube bank, and an air preheating tube bank. According tomy improved method, the anthracite coal is pulverized in contact with a stream of hot air preheated by. combustion gases from the generator and the resulting mixture of pulveriz ed anthracite. coal and air is passed intoone end of thecOmbustion chamber and therein burned at high temperature. 1

An important feature of my invention relates to the balancing of the draft in the. combustion chamber so as to maintainan ei'itremely high temperature inithe neighborhood ofthelourners to insure substantially complete combustion of the pulverized anthracite coal. The products of combustion resulting from this operation are conducted from the opposite end of the combustion chamber over the steam superheater tube bank, then over an economizer tube bank, and finally through an air preheater, the temperature or amount, or both, of the combustion gases contacted with the superheater bank being controlled automatically in response to variations in the temperature of the superheated steam, while the temperature of the combustion gases passed to the air preheater are controlled in response to any variation in the temperature of the preheated air.

The invention includes other control features which are described in greater detail hereinafter in connection with the accompanying drawing forming a part of this application.

The drawing comprises a single figure which is a diagrammatic vertical sectional view of a steam generator unit of the power plant type illustrating the features of my invention. In the drawing, certain parts are broken away or shown diagrammatically in order to simplify the illustration.

The steam generator unit shown in the drawing and which is used to illustrate my invention, is mounted on a suitable foundation or floor within a housing comprising side walls 12 and a roof I4. The unit is of substantially rectangular cross-section and is supported in the usual manner by suitable steel framework and columns according to the usual practice. The steam generator unit per se includes a steam and water drum I6 mounted in the upper part of the unit above but separated from a downdraft combustionchamber l8 which is preferably rectangular in horizontal cross-section. The chamber I8 is of relatively great height compared to its width, and is completely surrounded by side walls of steam generating tubes closely mounted together to form continuous tube walls. The combustion chamber I8 is provided with a roof 28 of refractory insulation substantially lined. with steaming tubes 22 which connect into the drum l8 and a header 24. The bottom of the combustion chamber includes refractory sloping walls which terminate in an ash pit 26 provided with a door 28 for the removal of ashes. The three outside walls of the combustion chamber [8 are of refractory 30, lined with tubes'32; The tubes 32 on the right wall connect between header 24 at the top and a header 34 at the bottom of the combustion chamber. The side wall tubes32 are mounted between an upper header and a lower header 38. Tubes 39 connect theheader to the drum [6. v

The left wall of the combustion-chamber "I8 is uninsulated and includes only a row of closely mounted tubes 40 which extend from thesteam and water drum lli to a lower header 42 and forms a partition between the combustion chamber and the adjacent chamber hereinafter referred to. Some of the tubes 48 are'bent out of line in the lower portion of the combustion chamber l8, as shown at 44, to permit the passage of combustion gases from the chamber.

The combustion gases from the chamber l8 pass into the lower portion of a chamber 48in which is mounted a steam superheating tube bank '48 having steam inlet lines 58'connected into the upper portion of the steam and water drum l6. superheated steam is discharged from the superheater bank 48 through a header 52.

4 Refractory baffles 54 extend between the tubes 48 and the bank 48 to direct combustion gases around the superheater tubes. Any ash settled out in the chamber 46 is collected in a receiver 58 and removed through a suitable valve as shown. The left side wall of thechamber 46 consists almost entirely of closely spaced steaming tubes 58 forming a partition between the superheater chamber and the adjacent chamber, hereinafter referred to, the steaming tubes being connected into the steam and water drum l6 and the header 42. At the upper part of the unit some of the tubes 58 are bent out of line at 60 thus forming a passage between the outlet of the superheater chamber and the adjacent chamber, hereinafter referred to to permit the flow of combustion gases from the upper part of the chamber 46 to the adjacent chamber. Alternate tubes 58 are also bent out of line at 82 at approximately the mid-height of the superheater bank 48, to form an opening in the partition formed by the tubes 58 to permit the bypassing of combustion gases to the adjacent chamber before they have passed entirely over the superheater bank. The control of gases at this point is accomplished by a pair of dampers 64 which are shown as mounted between the straight and bent-out tubes 58 but which may be arranged in any suitable manner to control the gas flow. The end walls of the chamber 46 are formed by an extension of the wall tubes 32 between headers 36 and 38. The unit includes outside downcomers from the'lower portion of the drum l6 which connect into the headers 34, 38 and 42, to provide the water circulation.

The combustion gases passing from the chamber 48 around the tubes at the point 60, are directed downwardly over an economizer tube bank 86 through which water is supplied to the unit and in which the feed water is heated to approximately the steaming temperature. A side wall 68 directs the combustion gases downwardly through the economizer bank 86, and any ash which may be settled out is collected in a receiver 61 and removed through a valve, as shown.

From the lower portion of the economizer bank 68, the combustion gases pass upwardly to the upper portion of the unit and then downwardly through air heating tubes III in an air preheater '12. The combustion gases discharged from the lower portion of the air preheater are connected through a flue duct 14 into an exhaust fan/I8 which exhausts the combustion gases from the unit and discharges them through a ductjl8 to a stack, not shown. Any ash settling out in the tubes 10 is collected in a receiver 88 and discharged through avalve, 'as'indicated. Provision is made for bypassing a portion of the combustion gases directly from the upper part of the chamber 48 to the air preheater 12, by means of a bypass damper 82 controlling the opening in a passage between the inlet of the economizer chamber and the inletv of the air preheatcr.

The air to be preheated in the heater I2 is forced by means of a fan 84 into the lower portion of the air preheater, wherein it passes around the tubes 18 so that it'is heatedby the 'hotzcombustion gases. The preheated air is discharged at the upper portion of the unit through a'duct system 88 which delivers the air to the. upp r part. of. the unit for supporting combustion in the combustion chamber. 18. A substantial pro- :portion of preheated air is conducted through a duct 88 into a c'oallchute 90 which deliversnoal to be pulverized and-hot air tothe inlet endot'a tube mill 92. The anthracitecoalto be pulverized and which is used for combustion in the steam generator unit in accordance with the preferred form of the invention is taken from a storage bin 94 through weighing and feeding, apparatus of known construction 96, and delivered into the chute S9. .The tube mill 92 is operated in the usual manner so as to pulverize the anthracite coal while the hot air stream delivered to the tube mill from the duct 88 picks up the pulverized coal and carries it through an outlet duct 98 into an exhaust fan Hill which aids in drawing the air of the desired quantity and proportion through the tube mill and which delivers the mixtureof hot air and pulverized coal through ducts I02 to pulverized coal burners I04 mounted in the upper portion of the combustion chamber l8. Hot secondary air is delivered to the burners l0; through valve controlled ducts 16 which connect into the main hot air supply duct 85.

The automatic means for controlling the operation of the steam generator unit of the present invention comprises a control element IE9 mounted in the upper portion of the combustion chamber l3 and connected through a line or-lines ME] to a control box I l2 which in turn is connected by lines H4 to the motor of the fan It. The control element I58 may be responsive to changes in the temperature or the pressure, or both, existing in the upper portion of the combustion chamber Hi. The control is preferably such that if the temperature or the pressure tends to fall below a given point or value, the fan will be slowed down so as to decrease the pull on the unit and thereby increase the pressure and temperature in the upper portion of the combustion chamber and cause a greater eddying of the hot combustion gases in the upper portion of the chamber is. The maintenance of the extremely high temperatures in the upper portion of the combustion chamber is essential for the economi cal and complete combustionof the pulverized anthracite coal. The control H18 preferably includes a pressure responsive means so that a balanced draft is kept in the unit, whilethe forced combustion feed and combustion temperature cause the eddying.

The control mechanism also includes an automatic means for operating the dampers 64 comprising a thermostatic control mechanism H6 connected into the dampers 64 and responsive to the temperature of the superheated steam in the header 52. The mechanism 1 I6 is set to maintain a predetermined temperature in the superheated steam and this mechanism functions to open or close the dampers 64 to vary: the proportion of hot combustion gases passing over the upper portion of the superheater tube bank :38. The dampers 54 are arranged so that the hot combustion gases passing therearound contact the lower portion. of the economizer 65 before passing on to the air preheater F2.

The control mechanism furthermore includes a thermostatic device H8 responsive to the temperature of the preheated air in the duct 86 and arranged to operate the bypass damper 82 through connecting lines or operating means 7128. In order to operate the steam generator-unit with pulverized anthracite coal, the air in the duct 86 must bemaintained ata temperature which is relatively'high compared with that necessary when operating with bituminous coal or other high volatile fuels. The arrangement-is thereforesuch that regardless of the amount of heat put into the economizer bank 66, the air temperature in duct 88 is maintained at the desired high temperature by bypassing combustion gases direct to the air preheater. It is apparent that the control means H6 and H8 will correlate to some extent with each other because the bypassing of considerable quantities of high temperature gases at the dampers 64 will naturally increase the temperature of the gases passing through air preheater 12. Accordingly; it may be stated that in general, as the dampers 64 are opened, the damper 82 will close. Furthermore. it will be understood that as the fan 16 is slowed down, there will be some alteration in the dampers 64 and 82, due to the decrease in the volume of combustion gases, although this effect may be, in part at least, offset by the fact that the com-V bustion gases may attain a slightly higher temperature because of the increase in temperature 7 in the upper part of the combustion chamber I8 In the carrying out of the improved method of the present invention, the combustion in the chamber 18 is conducted with such high temperature air and under such pressure balancing conditions that the temperature in the upper part of the combustion chamber is from 2700 to about 3=000 F., while that in the lower part of chamber isfrom 1860 to 2400" F. This provides a temperature in the chamber 46 of about 1700 F. or higher, while the gases passing at the point 60 toward the economizer 66 will have a temperature of approximately 1100 F. The various control means; for regulating the temperature of the preheated air are preferably set to operate so that the combustion gases entering into the air preheater. l2 Will have a temperature of at least 700 F. so that the air will have a temperature of 500 F. or higher.

In the utilization of relatively wet anthracite coal, the preheated air may have a somewhat higher temperature, and a greater proportion of the preheated air may be sent through the duct 88 to the tube mill. 1 have found that the use of relatively high temperature air in the tube mill facilitates the drying of the coal and thereby increases the grinding rate and degree of pulverization of thecoal. Furthermore, the use of preheated air of relatively hightemperature provides an efiective carrier for themoisture removed from the coal and delivers it through the various ducts at a temperature very substantially above that at which any moisture condensation will occur. I

The invention has been illustrated in connectiontwith a preferred form of apparatus and operation in which the various elements are arranged in a particular manner and in which certain specific directions for the flow of combustion gases have been given. It is to be understood, however, that the invention may be applied to steam generators and operations in which the combustion chamber is not fired at thetop. t g v The improved method and apparatus has also been described and illustrated in connection with the particular problem of burning anthracite coal. Other coals, such as bituminous coal, may be used and fluid fuels may also be employed, although lower ignition temperatures may suffree to initiate and complete their combustion.

The economizer tube bank 66 is adapted to preheat feed-water and provide a means for balancing or smoothing out the operation of the generator unit. Under extreme conditions, most of the combustion gases may bypass the economizer in order to provide the required quantity of superheated steam at the desired temperature and at the-same time provide an adequate supply of preheated air at a temperature necessary to maintain the advantageous high temperatures in the combustion chamber adjacent the burners. Under other conditions, the water in the economizer may be heated to a steaming temperature. The generator, however, may be balanoed so that the feed water is heated to a constant temperature in order to prevent the economizer bank from taking heat from other parts'of the generator unit.

-'The various control mechanism utilized in acconiance with the present invention have not been described in detail individually because such means are available'and commonly used in the control of other types of apparatus. From the foregoing description, it will be apparent that various changes may be made in the arrangement of "the various elements of the apparatus and their individual structures, without departing from the spirit of the invention. Such changes are contemplated as coming within the scope of the invention, as defined by the appended claims.

' What I claim is:

l; A steam generatorunit including a combustion chamber for producing high temperature combustion gases, an economizer chamber substantially parallel to said combustion chamber and having one of its ends substantially in line with the corresponding end of the combustion chamber, an economizer tube bank mounted in said economizer chamber and having upper and lower ends, a superheater chamber between and substantially parallel to the combustion chamber and the economizer chamber and having its end corresponding to said end of the combustion chamber substantially in line therewith, a steam superheater tube bank mounted in the superheater chamber and having upper and lower ends, said combustion chamber and said superheater chamber being defined in part by first partition means separating the combustion chamber from the superheater chamber, said economizer chamber and said superheater chamber being defined in part by second partition means separating the economizer chamber from the superheater chamber, an air pre'heater, the combustion chamber having an outlet opening into the end opposite said corresponding end of the superheater chamber for delivering combustion gases to the superheater chamber, first passage means between said corresponding end of the superheater chamber and said one end of the economizer chamber for delivering combustion gases to the economizer chamber after passing in heat exchange with the superheater 'tubebank, means for-delivering combustion gases from the-opposite endof the economizer chamber to the inlet of the air preheater, said second partition means having an opening located between said upper and lower ends of the superheater tube bank and said upper and lower ends of the economizer tube bank for conducting combustion gases iroln the superheater chamber to the economizer chamber after passing over only a portion of the superheater tube bank, means for varying the flow of combustion gases through said opening in said second partition means, second passage means extending directly between said first passage means and the inlet of the air preheater, whereby combustion gases passing through said second passage means bypass the economizer tube bank, and means for varying the flow of combustion gases through said second passage means.

2. A steam generator comprising a combustion chamber for producing high temperature combustion gases, an economizer chamber substantially parallel to said combustion chamber and having one of its ends substantially in line with the corresponding end of the combustion chamber, an economizer tube bank mounted in said economizer chamber and having upper and lower ends, a superheater chamber between and substantially parallel to the combustion chamber and the economizer chamber and having its end corresponding to said end of the combustion chamber substantially in line therewith, a steam superheater tube bank mounted in the superheater chamber and having upper and lower ends, said combustion chamber and said superheater chamber being defined in part by first partition means separating the combustion chamber from the superheater chamber, said economizer chamber and said superheater chamber :being defined in part by second partition means separating the economizer chamber from the superheater chamber, an air preheater extending substantially parallel to said economizer chamber and on the side thereof remote from theshperheater chamber, means for supplying fuel'to the combustion chamber, means .for buming said fuel in the combustion chamber, the combustion chamber having an outlet opening into thesuperheater chamber at the end opposite said corresponding end .of the superheater chamber'for delivering combustion gases to the superheater chamber, first passage means between said corresponding end of the superheater chamber and said one end of the economizer chamber for delivering combustion gases to the economizer chamber, means for delivering combustion gases from the opposite end of the economizer chamber to the inlet :of the air preheater, means for delivering air heated insaid air preheater to said fuelssupply means to heat said fuel and carry it to the combustion chamber, said second partition means having an opening located between said upper and lower ends of the superheater tube bank and said upper and lower ends of the economizer tube bank for delivering combustion gases which have passed over only a portion oi said superheater tube bank to said economizer chamber, means .for varying the flow of combustion gases through said opening in said secand partition means, second passage means extending direcitly between said first passage means and the inlet of the air 'preheater, whereby gases passing 'Tthrough said secondpassage means bypass the economizer tube bank, and means for varying the flow of combustion gases through said second passage means.

3. .A-steamgeneratorrheated by pulverized coal comprising'a combustion chamber for producing high temperature :combustion rgases, an economizer chamber substantially parallel to said combustion chamber and having one .of its ends substantially line with the 'earresponding end of ithewcombustion chamber, an economizer tube bankimounted insaid economizer chamber and having upper and lower ends, a super heater :chamber 'between and substantially paralleltoithe combustion chamber and the economizer chamber and having its end corresponding to saiidcend ofithezcombustion chamber substantially iniine therewith,;aisteam superheater tube bank mounted the superheater chamber and havingupper nndlower'ends, said combustion chamher and said superheater chamber being defined in part by first partition means separating the combustion chamber from the superheater chamber, said superheater chamber and said economizer chamber being defined in part by second partition means separating the economizer chamber from the superheater chamber, an air preheater extending substantially parallel to said economizer chamber and on the side thereof remote from the superheater chamber, means for supplying pulverized coal to the combustion chamber, means for burning said pulverized coal in the combustion chamber, the combustion chamber having an outlet opening into the superheater chamber at the end opposite said corresponding end of the superheater chamber for delivering combustion gases to the superheater chamber, first passage means between said corresponding end of the superheated chamber and said one end of the economizer chamber for delivering combustion gases to the economizer chamber, means for delivering combustion gases from the opposite end of the economizer chamber to the inlet of the air preheater, means for delivering air heated in said air preheater to said pulverized coal supply means to heat said coal and carry it to the combustion chamber, said second partition means having an opening located between said upper and lower ends of the superheater tube bank and said upper and lower ends of the economizer tube bank for delivering combustion gases which have passed over only a portion of said superheater tube bank to said economizer chamber, means responsive to the temperature of steam in said superheater tube bank for increasing the flow of combustion gases through said opening in said second partition means when the temperature in the superhcater tube bank increases and for decreasing the flow of combustion gases through said opening in said second partition means when the temperature in the superheater tube bank decreases, second passage means extending directly between said first passage means and the inlet of the air preheater, whereby gases passing through said second passage means by-pass the economizer tube bank, and means responsive to th temperature of the preheated air for increasing the flow of combustion gases through said second passage means directly from the superheater chamber to the air preheater when the temperature of the preheated air decreases and for decreasing the flow of combustion gases through said second passage means directly from the superheater chamber to the air preheater when the temperature of the preheated air increases.

JOHN V. PYLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,450,693 McLean Apr. 3, 1923 1,820,939 Gibson Sept. 1, 1931 2,170,345 Bailey et a1 Aug. 22, 1939 2,243,913 Marshall June 3, 1941 2,298,700 Junkins et al. Oct. 13, 1942 2,349,329 Anderson May 23, 1944 2,386,188 Artsay Oct. 9, 1945 2,392,325 Kuhner Jan. 8, 1946 FOREIGN PATENTS Number Country Date 454,408 Germany Jan. 7, 1928 

